The phrase "to sift the flour" means to pass the flour through a sifter or sieve to remove any clumps or impurities.
Sentences with «to sift the flour»
To make the pastry, sift the flour into a mixing bowl and rub or cut in the butter until the mixture resembles fine breadcrumbs. (mycookinggallery.blogspot.ru)
Lightly sift flours with a fork to break up any lumps. (vegweb.com)
In separate bowl sift flour, almond meal, and powdered sugar together. (thebeautifulbalance.com)